Shuitsu Harada

Functional Properties of Jaw and Tongue Muscles in Rats Fed a Liquid Diet after Being Weaned

Decreased masticatory demands due to liquid or soft diets cause a reduction in the growth of craniofacial bones and in the development of feeding musculature, but the effects on masticatory function and jaw/tongue muscle activities are unclear. The present study was undertaken to test the hypotheses that a liquid diet feeding after weaning affects the critical-period programming of mastication and the motor performances of jaw and tongue muscles. Thirty-six male Wistar rats were divided into two equals groups at weaning and fed either a solid (solid-diet group) or a liquid (liquid-diet group) diet until they reached 50 days of age. Electromyograms (EMG) of the masseter, medial pterygoid, temporalis, anterior digastric, styloglossus, and genioglossus were recorded while animals were naturally ingesting ordinary pellets, apple cubes, and a liquid diet. It was found that: (1) a more irregular chewing rhythm, a shorter chewing sequence, and a longer chewing cycle were found in the liquid-diet group, but there were no differences observed during lapping/licking between the two groups; (2) during the chewing cycles, the EMG onset of each muscle in relation to that of the masseter in the liquid-diet group was similar to that in the lapping/licking cycles in both groups; (3) the activities of jaw elevators (masseter, medial pterygoid, and temporalis) during the chewing cycles were significantly higher in the liquid-diet group; and (4) the increase in the EMG activities of jaw elevators during pellet chewing compared with apple cube chewing was significantly weaker in the liquid-diet group, whereas such an enhancement was found simultaneously in the styloglossus in the solid-diet group, and in the anterior digastric in the liquid-diet group. These findings verify that: (1) the motor output of jaw and tongue muscles may be altered in rats fed a liquid diet after being weaned; (2) the feeding of a liquid diet to rats after being weaned may obstruct the functional transition from suckling to mastication; and (3) jaw elevators that develop without motor learning of mastication are inefficiency when performing functionally.

Maturation of taste buds on the soft palate of the postnatal rat

Taste bud distribution on the soft palate and within three types of tongue papillae (fungiform, foliate, and circumvallate) were examined histologically in the rat at different postnatal ages. After paraffin embedding, serial sections (10 microm) were made and stained by HE, and digitized images of each section were examined. The existence of a taste pore was used to identify mature taste buds. At birth, 53% (68 of 127 observed) of the taste buds on the soft palate, but only 14% (14 of 110 observed) within fungiform papillae, contained a taste pore. One week after birth, the number of mature taste buds increased rapidly, resulting in 90% of soft palate taste buds and 80% of fungiform taste buds containing taste pores. In contrast, no taste buds with pores were observed at birth within foliate and circumvallate papillae; however, at two weeks after birth 52% (71 of 132 observed) of the foliate and 68% (180 of 267 observed) of the circumvallate taste buds examined contained taste pores. These results suggest that taste buds within the soft palate play an important role in the detection of nutrients in the neonatal rat.

Gustatory specificity for amino acids in the facial taste system of the carp,Cyprinus carpio L.

Summary1.The stimulatory effectiveness of amino acids and analogs on the external gustatory receptors of the carp (Cyprinus carpio L.) was investigated with extracellular electrophysiological techniques.2.Amino acids are highly effective stimuli for the carp gustatory system. Threshold for L-proline, the most effective stimulus tested, averaged 10−8.5±0.9 (SD) mol/l. Thresholds for the other stimulatory chemicals ranged between 10−4–10−8 mol/l (Table 1). Averaged gustatory neural activity for L-proline and L-alanine increased with logarithmic increase in stimulus concentration over a wide concentration range (approximately 6–7 log units) and showed a tendency for saturation at concentrations ≧ 10−3 mol/l (Figs. 5 and 6).3.The external taste system of the carp responded to neutral and acidic amino acids, but not to basic ones.4.Taste responses to amino acids were highly stereospecific; the L-isomer of an amino acid was stimulatory, but the enantiomer was not (Table 2). The gustatory receptors were highly responsive to amino acids containing 3 to 4 carbon atoms having unbranched and uncharged side chains. Further, this study indicated that the α-amino group and the α-hydrogen were essential for maximal effectiveness, and that for some amino acids on ionically charged primary carboxyl group was generally unnecessary for a maximal receptor response (Table 3).5.The molecular requirements of the neutral amino acid receptor sites for the external gustatory system in the carp appeared to be similar in general to those described in the channel catfish (Caprio 1978).6.Due to the limited number of stimulatory amino acids, the taste receptor in the carp shows a more narrowly-tuned chemical spectrum than does the olfactory system in the same species. Additionally, the taste system of the carp is more sensitive to amino acids than the olfactory system in the same species (Table 1; Goh and Tamura 1978).

High sensitivity of minnow gustatory receptors to amino acids

Abstract The stimulating effects of amino acids and related compounds on the gustatory receptors were studied in the Japanese minnow, Pseudorasbora parva , by recording electrical responses from the palatine nerve innervating the upper lip and the adjacent palate. All of the 21 amino acids and 6 related compounds elicited responses at a concentration of 10 −3 M. The order of the response magnitude to the 6 most effective of 18 L-amino acids was: proline > lysine-HCl > alanine > arginine-HCl > cysteine > serine. The threshold concentration for proline, the most potent among the amino acids was estimated to range between 10 −11 and 10 −10 M. The relationship between the log response magnitude and the log stimulus concentration for L-proline or L-alanine was linear in a relatively wide concentration range, showing a tendency for the response to be saturated at higher concentrations. The results of this study indicate that the amino acids are the most potent gustatory stimuli in the Japanese minnow among various chemicals so far tested including salts, sugars, quinine-HCl and ribonucleotides.

Sonic hedgehog-expressing basal cells are general post-mitotic precursors of functional taste receptor cells.

Background: Taste buds contain ∼60 elongate cells and several basal cells. Elongate cells comprise three functional taste cell types: I, glial cells; II, bitter/sweet/umami receptor cells; and III, sour detectors. Although taste cells are continuously renewed, lineage relationships among cell types are ill‐defined. Basal cells have been proposed as taste bud stem cells, a subset of which express Sonic hedgehog (Shh). However, Shh+ basal cells turn over rapidly suggesting that Shh+ cells are post‐mitotic precursors of some or all taste cell types. Results: To fate map Shh‐expressing cells, mice carrying ShhCreERT2 and a high (CAG‐CAT‐EGFP) or low (R26RLacZ) efficiency reporter allele were given tamoxifen to activate Cre in Shh+ cells. Using R26RLacZ, lineage‐labeled cells occur singly within buds, supporting a post‐mitotic state for Shh+ cells. Using either reporter, we show that Shh+ cells differentiate into all three taste cell types, in proportions reflecting cell type ratios in taste buds (I > II > III). Conclusions: Shh+ cells are not stem cells, but are post‐mitotic, immediate precursors of taste cells. Shh+ cells differentiate into each of the three taste cell types, and the choice of a specific taste cell fate is regulated to maintain the proper ratio within buds. Developmental Dynamics 243:1286–1297, 2014.

Expression of the basal cell markers of taste buds in the anterior tongue and soft palate of the mouse embryo

Although embryonic expression of Shh in the fungiform papilla placodes has a critical role in fungiform papilla patterning, it remains unclear whether its appearance indicates the differentiation of the basal cells of taste buds. To examine the embryonic development of the basal cells, the expression of Shh, Prox1, and Mash1 was determined in the anterior tongue and soft palate in mouse embryos by in situ hybridization. In the anterior tongue, Prox1 was coexpressed with Shh from the beginning of Shh expression in the fungiform papilla placodes at E12.5. Shh was expressed in the soft palate in a band‐like pattern in the anteriormost region and in a punctate pattern in the posterior region at E14.5. The number (21.4 ± 4.3, at E14.5) of locations where Shh was observed (i.e., spots) rapidly increased and reached a peak level (54.8 ± 4.0 at E15.5). Also in the soft palate, Prox1 was coexpressed with Shh from the beginning of Shh expression. These results suggest that basal cell differentiation occurs synchronously with the patterning of Shh spots both in the anterior tongue and in the soft palate. In contrast, Mash1 expression lagged behind the expression of Shh and Prox1 and began after the number of Shh spots had reached its peak level in the soft palate. Furthermore, immunohistochemistry of PGP9.5 and Shh revealed that epithelial innervation slightly preceded Mash1 expression both in the tongue and in the soft palate. This is the first report describing the time courses of the embryonic expression of basal cell markers of taste buds. J. Comp. Neurol. 509:211–224, 2008.

Marine teleost locates live prey through pH sensing

Hold your breath or the catfish will find you Finding prey is hard enough in the light of day, but animals that are nocturnal or live in murky conditions face even greater challenges. Caprio et al. describe a sense that allows a marine catfish to detect the mere “breathing” of their prey target. External sensors on the catfishs whiskers detect pH changes generated by hidden, respiring polychaete worms. Science, this issue p. 1154 Japanese eel catfish whiskers help to locate hidden worms by sensing pH increases associated with respiration. We report that the Japanese sea catfish Plotosus japonicus senses local pH-associated increases in H+/CO2 equating to a decrease of ≤0.1 pH unit in ambient seawater. We demonstrated that these sensors, located on the external body of the fish, detect undamaged cryptic respiring prey, such as polychaete worms. Sensitivity is maximal at the natural pH of seawater (pH 8.1 to 8.2) and decreases dramatically in seawater with a pH <8.0.

Gα-gustducin Is Extensively Coexpressed with Sweet and Bitter Taste Receptors in both the Soft Palate and Fungiform Papillae but Has a Different Functional Significance

To clarify the regional differences in the expression and functional significance of Gα-gustducin in soft palate (SP) and fungiform (FF) taste buds, we examined the coexpression of Gα-gustducin with taste receptors and the impact of Gα-gustducin knockout (gKO) on neural responses to several sweet and bitter compounds. Sweet responses from both the greater superficial petrosal (GSP) and chorda tympani (CT) nerves in gKO mice were markedly depleted, reflecting overlapping expression of Gα-gustducin and Tas1r2. However, although Gα-gustducin was expressed in 87% and 88% of Tas2rs cells in the SP and FF, respectively, there were no statistically significant differences in the CT responses to quinine-HCl (QHCl) and denatonium (Den) between gKO and wild-type (WT) mice. In contrast, GSP responses to these compounds were markedly reduced in gKO mice with an apparent elevation of thresholds (>10-fold). These results suggest that 1) Gα-gustducin plays a critical role in sweet transduction in both the SP and the FF, 2) other Gα subunits coexpressed with Gα-gustducin in the FF are sufficient for responses to QHCl and Den, and 3) robust GSP responses to QHCl and Den occur in the SP by a Gα-gustducin-dependent mechanism, which is absent in the FF.Like mammals, bird embryos are capable of chemosensory learning, but the ontogeny of their feeding preferences has not been examined. We tested if the timing of stimulation in chicken embryos modulates the impact of in ovo olfactory stimulation on later food preferences. We exposed chicken embryos to an olfactory stimulus for a 4-day period in the middle or toward the end of the incubation period. The chicks were tested for their preference between foods with and without the olfactory stimulus in 3-min choice tests and on a 24-h time scale. Regardless of the type of food (familiar or novel) or the duration of the test, the control chicks not exposed to the olfactory stimulus consistently showed significant preferences for non-odorized foods. Chicks that were exposed in ovo to the olfactory stimulus did not show a preference for odorized or non-odorized foods. Only those chicks that were exposed to the olfactory stimulus toward the end of the incubation period differed from the controls and incorporated a higher proportion of odorized food into their diets on a 24-h time scale. This result indicates that olfactory stimulation at the end of embryonic development has a stronger impact on later feeding preferences. Our findings contribute to the growing pool of recent data appreciating the impact of olfactory signals on behavior regulation in avian species.

During development intense Sox2 expression marks not only Prox1-expressing taste bud cell but also perigemmal cell lineages

Sox2 is proposed to regulate the differentiation of bipotential progenitor cells into taste bud cells. However, detailed expression of Sox2 remains unclear. In this report, Sox2 expression during taste bud development in the fungiform (FF), circumvallate (CV) and soft palate (SP) areas is examined together with Prox1. First, we immunohistochemically checked Prox1 expression in adults and found that almost all taste bud cells are Prox1-positive. During FF development, intense Sox2 expression was restricted to taste bud primordia expressing Prox1 at E12.5. However, at E14.5, Sox2 was intensely expressed outside the developing taste buds resolving to perigemmal Sox2 expression in adults. In the SP, at E14.5, taste bud primordia emerged as Prox1-expressing cell clusters. However, intense Sox2 expression was not restricted to taste bud primordia but was detected widely in the epithelium. During development, Sox2 expression outside developing taste buds was generally down-regulated but was retained in the perigemmal region similarly to that in the FF. In the CV, the initial stage of taste bud development remained unclear because of the lack of taste bud primordia comparable to that in the FF and SP. Here, we show that Prox1-expressing cells appear in the apical epithelium at E12.5, in the inner trench wall at E17.5 and in the outer trench wall at E18.5. Sox2 was again not restricted to developing taste bud cells expressing Prox1 during CV development. The expression patterns support that Sox2 does not serve as a cell fate selector between taste bud cells and surrounding keratinocytes but rather may contribute to them both.

Neural and Behavioral Responses to Amino Acids in Mice and Rats

In order to clarify the gustatory effectiveness of amino acids, responses were examined using electrophysiological and behavioral methods in the mouse and rat. Electrophysiological experiments on the chorda tympani nerve have revealed that amino acids are classified into at least three groups according to basic (BA), neutral (NA), and acidic amino acids (AA). The chorda tympani rsponses to both Land D-BA hydrochloride salts (BA-HCl) in each animal were similar to those for NaCl, and adapted well with those for monovalent chloride salts but not with NA or sucrose in the cross-adaptation experiment’ (see FIG. 1). Several structural analogues or derivatives of L-Arg and LLys were tested, to show that the a-amino group is essential for the strong stimulatory effectiveness of BA-HCl, although the BA of free-base form was less stimulatory than the corresponding HCl salts. Larger responses were elicitied when the pH of the solutions was lowered. A similar effect of lowering pH was also observed for NA and other substances that have more than one amino group. These results suggest that the charged amino group in the organic substances plays an important role in producing their strong effect. The relative stimulatory effectiveness of L-NA was larger in mice than in rats, and that for L-isomers was significantly larger than D-isomers in both species. Responses to these NA cross-adapted with sucrose, but not with NaCl or BA. The response characteristics of AA were similar to that for HCl.